Methyl acrylate irreversibility

Pasto and colleagues studied the stereochemical features of the [2 + 2] cycloadditions of chiral allenes. The formation of a diradical intermediate in the cycloadditions of enan-tiomerically enriched 1,3-dimethylallene (10) with acrylonitrile (11a) and methyl acrylate (lib) (equation 4) was shown to be irreversible. 1,3-Dimethylallene recovered from the reaction mixture was shown to have the same ee as the starting material. Interestingly,... 

One case, however, is clear—ammonia and amines react with ordinary esters to give amides, and it is known that the attack at the carbonyl group is ratedetermining and effectively irreversible above pH 7. Ammonia (neutral and therefore a relatively soft nucleophile) reacts in methanol with methyl acrylate 4.80 kinetically at the 3 position to give the primary amine 4.81, and reaction continues in the same sense to give successively the secondary amine 4.82 and tertiary amine 4.83. 

Methylation and benzylation of the pyrrolidine dienamine of 3-methyl-A "-2-octa-lone gives a mixture of N- and jS-alkylated products in protic and aprotic solvents. However, the position of attack by acrylonitrile and methyl acrylate is solvent-dependent. In protic solvents the / -alkylated octalone is obtained on hydrolysis, whereas in aprotic solvents the -alkylated product is produced (Scheme 7). This change in the regioselectivity arises from the C-3 methyl group being forced into a quasi-axial orientation because of allylic strain in the equatorial orientation. As a consequence the carbanionic centre in the initially formed zwitterion 6 cannot be neutralized by an internal proton transfer of an axial proton at C-3. In protic solvents intermolecular protonation renders the reaction irreversible, but in aprotic solvent reversion to starting material occurs. This allows 5- or -alkylation to occur and this is rendered irreversible by internal proton transfer from the 6 - or 5-position, respectively, to the carbanionic centre in the resulting zwitterion (Scheme 7). 

Ammonia, a soft nucleophile for being neutral, reacts with methyl acrylate 100 in methanol in conjugate manner to give the primary amine 101. The reaction continues in the same sense and the secondary amine 102 and the tertiary amine 103 are formed successively [39]. It is to be noted that ammonia, and other primary and secondary amines, do not react with simple esters to form amides. Combine this with the known observation that attack at the carbonyl group is irreversible and also rate determining [40], the above conjugate addition must necessarily be a product of kinetic control, supported by HOMO-LUMO interaction. 

Thus, performing the activation in the presence of radically polymerizable alkenes leads to the first examples of well-defined AB or ABA-type PVDF-block copolymers with styrene (e, e ), butadiene (f, f, vinyl chloride (g, g ), vinyl acetate (h, h ), methyl acrylate (i, i, i"). and acrylonitrile (j, j ), initiated from both the PVDF halide chain ends. While here Mn2(CO)io simply performs irreversible halide activation, and there is no IDT, control of the block copolymerization can be envisioned by other CRP methods. 

The Michael addition of methyl a-acetamidoacrylate (196) with pyrrole (1) under silica-supported Lewis acid (Si(M) Si(Zn), Si(Al) and Si(Ti)) assisted by microwave irradiation (MW) afforded the alanine derivatives 395 and 396 dependent on the reaction conditions (Scheme 81) [153]. Both MW and thermal activation for pyrrole gave only Michael product 396, whereas alanine derivatives 395, which are the a-Michael addition product, and 396 were observed with A1 and Ti-catalyst. This behavior shows that aluminium and titanium Lewis acids can form a new acceptor in an irreversible way. The Si(M) or p-TsOH catalyzed reactions of N-benzylpyrrolc 397 with the acrylate 196 under MW gave the product 398 as sole product. The reaction yield has been increased by using a catalytic amount of p-TsOH (Scheme 82). 

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